Amplifiers are commonly used in an electronic device for enhancing the characteristics of the electronic device, such as gain, bandwidth and linearity. The vast application range of amplifiers includes active filters, buffers, analog-to-digital converters (ADCs), and radio frequency (RF) transceivers. In wireless communication systems, a power amplifier is an essential component in RF circuits. Power amplifiers are normally arranged on the front-end of an antenna transmitter for enlarging the amplitude of output signals.
RF surge refers to a rapid change in the peak of RF signals which occurs within a very short period of time in a circuit. When an electronic device (such as a power amplifier) is plugged in into a power outlet or when there is an impedance mismatch present in the system, a sudden increase or decrease may occurs in the operational or bias voltage/current of the electronic device. Although the duration of an RF surge signal is normally very short, it brings negative impacts, such as excessive voltage/current, which may permanently damage the internal devices of sensitive electronic devices.
Also, voltage standing wave ratio (VSWR) is a parameter for evaluating the performance of power amplifiers. VSWR is defined as the ratio between reflected power and input power. When the impedance of a device is larger or smaller than another connected device in the RF system, power is reflected at the place of mismatch, which creates standing waves along the transmission line and causes power return loss. If the VSWR is equal to the ideal value of 1.0, there would be no reflected power and the voltage would have a constant magnitude along the transmission line. A larger VSWR results in a larger reflected power and causes larger return loss. In real application, an imperfect VSWR not only weakens signal strength, the reflected power may also damage the internal devices of the electronic device.
Therefore, there is a need for a power amplifier capable of reducing the negative impact caused by surge or VSWR for use in an RF active circuit.